Metal shaping tools, such as cut-off and turning tools, which are mounted on a lathe turret or a similar tool carrier, are subjected to very strong distorting and deflecting forces, arising from the interaction of the cutting element and the metallic workpiece. The high speed demanded by lathe tool operations produces rapid vibrations which tend to change the accurate alignment of the tool's cutting edge and which make it difficult to reproducibly perform work at close tolerances. In particular there is a problem in setting tools at a specific angle to the workpiece after they have been removed for regrinding or sharpening. The release of screws to remove a tool bit for replacement is inefficient and time consuming. The positioning of tools by manual calibration is potentially affected by error on the part of the tool setter, and the provision of lateral guiding or supporting surfaces on the tool itself often introduces additional distortions by the uneven distribution of the hold of such devices, and the unequal pressure on the bearing surfaces. These drawbacks, singly or jointly, are especially onerous for low-cost, small-batch processing which requires fast set-ups without loss of accuracy. An additional problem relates to the much higher costs attendant the use of 1/2 inch cutting tools as compared to 3/8 tools, but misalignment occurs when one attempts to substitute 3/8 inch tools on a lathe designed for 1/2 inch tools.
The present invention is directed to resolve the various problems inherent in conventional designs by providing a tool holder for a metal cutting tool which permits the rapid and reproducibly accurate positioning of a tool relative to a rotating workpiece, and means for retaining the tool in the selected alignment therewith. Additionally, the tool holder is designed so as to use 3/8 inch tools but can be readily converted for a 1/2 inch lathe design when required.
The foregoing problems are overcome by the present invention directed to a tool holder for a lathe, releasably mounted on a lathe turret for linear and pivotable motion about a vertical bolt reclined in the confines of a vertical bore of oblong cross-section traversing the tool holder. The bolt has one of its ends engageable in a groove formed in the lathe turret and includes means for supporting a tool projecting outwardly from the tool holder to operate on a workpiece rotating about an axis. In accordance herewith, means are provided for releasably positioning the tool holder with respect to the turret including at least one pair of dowels, each dowel releasably inserted and depending from one of a plurality of aligned holes therefor vertically defined at predetermined locations through the tool holder. The angular orientation of the holes marked by the inserted dowels, relative to the rotation of the workpiece, defines a predetermined alignment of the tool holder on the turret.
More specifically, the cutting tool holder, according to the present invention, includes a massive, substantially block-like body which is vertically traversed by a bore of oblong, slot-like cross section. A T-bolt, passed through the bore, slidably fits at one of its ends into a T-shaped groove formed as a cross-slide on a lathe turret, as is well known in the art. At its opposite end, the T-bolt is secured against displacement by threaded means, tightened against the surface wall of the tool holder on both sides of the slot. A horizontally aligned, outwardly open recess on one of the vertical faces of the tool holder supports therein a portion of the shank of a cutting tool, which is firmly held in place therein by overhead screws admitted through vertical bores and bearing against the upper surface of the shank. In a cut-off tool holder formed in accordance with my copending application Ser. No. 681,971, filed Apr. 30, 1976, entitled "LATHE TOOL," the shank-supporting recess is formed by a shoulder in the face of the tool holder block, and a parallel shoulder in an overhead clamping lid which is pivotable about a hingepin. In another embodiment of the present invention the shank of a turning tool is supported, over a portion of its length, in an outwardly open, rectangular channel formed in the tool holder block.
A plurality of vertically extending, identical cylindrical holes are defined through the tool holder in two parallel rows, one on each side of the oblong bore slot. Locking pins, formed as dowels, with retaining snap rings, are releasably and slidingly received in the holes and protrude therefrom at at least one of their ends. The snap rings are adjustable and are removably mounted on the dowels to maintain them in a vertical position in the holes, and to prevent their displacement therefrom in the longitudinal direction.
In one embodiment of the present invention the holes in each row which are laterally equidistant from one another, are also equidistant from the opposite front and rear walls of the tool holder, so that the lines connecting pairs of transversely positioned holes are parallel to the respective walls. In another embodiment the two rows of holes are offset relative to one another by a predetermined distance, so that a line which connects, for example, the two holes at the ends of each row, describes an angle of less than 90.degree. with respect to the direction of the front and rear walls of the tool holder. Two dowels, each inserted in one cavity in each row, serve to rapidly and easily denote a particular orientation of the tool holder relative to the turret. Since the tool holder may be advanced or retracted, as well as rotated about the bolt with respect to the turret, the multiplicity of holes and the variety of angular settings which can be achieved by the placement of the dowels permits a large number of different alignments of the tool holder adapted for specific operations. A cut-off tool, for instance, intended to approach a rotating workpiece at an angle of 90.degree. relative to the axis of rotation, is advantageously held in a tool holder set at a 45.degree. angle with respect to the lathe turet, whereas a turning tool, also intended to maintain a 90.degree. approach angle, can satisfactorily perform if the tool holder is set at 90.degree. to the axis of rotation of a workpiece.
Once the dowels have been put in place, they may be retained in the respective holes during removal, replacement or adjustment of the tool holder and/or the tool carrier thereon, so that subsequent operations may be carried out at precisely the same angle. Likewise, tool holders may be interchanged in response to different cutting jobs, different dimensions or surface characteristics of the workpiece or different lengths of the workpiece, without sacrificing the accuracy of any operation. In addition to their function as positioning means the dowels serve as stops, limiting the deviation of the tool holder from its pre-set alignment.
In regard to the aforementioned substitution of 3/8 inch tools for 1/2 inch tools, this is accommodated by designing the tool holder so that the lower surface of the tool retaining channel is coplanar with the mounting surface of the tool holder. A shim can be inserted to raise the lower channel surface sufficiently so that a 3/8 inch tool can be used on lathe turrets designed for 1/2 inch tools.